Figure 2

H5 avian and H9 swine HA structures compared with H3 HA and HEF. (A) Ribbon diagram of the trimer of H5 (A/Dk/Sing/97) avian HA coloured by subdomains: receptor subdomain R (blue), vestigial enzyme subdomain E' (yellow), HA2 stem F subdomain (red), F' subdomain HA1 1–52 (pink), F' subdomain HA1 275–307 (purple). Oligosaccharides are coloured by atom type. (B) Trimer of H9 swine (A/Sw/9/98) HA. (C) Monomer of H5 (A/Dk/Sing/97) avian HA. Helix A and B, the interhelical loop between them, and the fusion peptide in HA2 are labelled. N1 and C1 indicate the termini of HA1; N2 and C2, those of HA2. The trimer axis, receptor-binding site and two prominent antigenic loops, 140s and 150s, are labelled. Residue numbers mark oligosaccharides, which are coloured by atom type. Carbohydrate attachment sites are at HA1 21, 33, 169 and 289, and at HA2 154. (D) Monomer of the H9 (A/Sw/9/98) swine HA. The x marks the deleted 140s loop. Carbohydrate attachment sites are at HA1 21, 128, 210, 289 and 296, and at HA2 154. (E) Monomer of trimeric H3 (A/Aichi/2/68) human HA (Wilson et al., 1981). Carbohydrate attachment sites are at HA1 8, 22, 38, 81, 165 and 285, and at HA2 154. (F) Monomer of trimeric influenza C virus (C/Johannesburg/1/66) haemagglutinin–esterase–fusion (HEF) protein (Rosenthal et al., 1998; Zhang et al., 1999). These figures and Figures 3B, 4A, B and D were generated using MOLSCRIPT and BOBSCRIPT (Kraulis, 1991; Esnouf, 1997).